d Estimate based on established active jobs for licensed
and unlicensed personnel aboard oceangoing ships of 1,000 gross-tons and over,
privately owned and operated, government-owned ships under bare boat charters,
ship managers and General Agency Agreement, supplemented by Military Sealift
Command employment totals for ships with Civil Service crews.

e The U.S. Coast Guard changed its methodology for
counting the number of recreational boats. Figures cited represent number of
numbered boats, not estimates as previously noted for 1960 and 1970.

f Does not include intraterritorial traffic (traffic
between ports in Puerto Rico and the Virgin Islands, which are considered a
single unit).

g Mobile Offshore Drilling Units.

h The international water freight operating revenues
data was revised in Transportation in America 1998 for all years except
1994 and 1996. Therefore, the international water freight data for years 1994
and 1996 may not be comparable to other years.

i Data is current as of January 1 of the following
year with the exception of 1999 data, which is current as of Apr. 1, 1999. Due
to a change in the source's periodicity, the data for 1999 is not comparable
to the data from years prior to 1999.

j 1992-2000 data come from the Marine Safety Management
Information System. Data for prior years may not be directly comparable.